A deformation sensor is known from German Patent Application No. 42 20 270 A1. Such a deformation sensor, which includes an optical transmission medium having transmission and reception elements coupled to it, is particularly to be used for detecting deformations of the vehicle body which a vehicle undergoes in the event of a crash. Such an optical deformation sensor can preferably be used for detecting side crashes in vehicles. An optical transmission medium, which includes an optical waveguide as in the specification cited, changes its light transmission properties due to the microbending effect upon curving such as that which occurs in the event of a deformation of the vehicle body. Specifically, the intensity of the light transmitted changes if the optical waveguide undergoes a curvature due to a deformation of the vehicle body part onto which the optical waveguide is affixed.
As described in U.S. Pat. No. 5,917,180, the optical transmission medium of a deformation sensor includes a deformable, light-transmitting body, made of, for example, polyurethane foam. The optical scattering properties of this deformable, light-transmitting body change if pressure is exerted on it, which occurs, for example, in the event of a deformation of the vehicle body part onto which the body is affixed.
In order to avoid spurious trippings of restraint devices (airbags, seat belt tightening system, roll cage, etc.) caused by the crash sensor in the vehicle, and also to avoid faulty non-tripping in the event of a crash, continuous function checking of the deformation sensor is necessary. The related art in this connection is the use of at least one further sensor of another type—this can be, for example, an acceleration sensor which is positioned in addition to the deformation sensor at any other location in the vehicle. As described in German Patent No. 42 20 270, the function checking can also be performed using a second identical deformation sensor. In each case, a further supplementary sensor must be located in the vehicle.
An object of the present invention therefore is to provide a deformation sensor of the type described above in which no further supplementary sensor is necessary for its function checking.